The Laser Guide Star Facility (LGSF) of GTC will generate a laser guide star (LGS) in the high atmosphere for the GTC Adaptive Optics System (GTCAO) to measure and correct the effect of the atmospheric turbulence. The GTCAO LGS Wavefront Sensor (LWS) will be based on a Shack Hartmann WFS and placed on the GTCAO optical bench, where the Natural Guide Star (NGS) Wavefront Sensor is already installed. The science dichroic splits the light beam so that the visible range (0.47-0.9μm) is reflected to the NGS WFS, and the infrared range 0.9-2.5μm is transmitted to the science instrument. A new second dichroic (LWS DC) will be installed in the visible path, to reflect 589nm (FWHM 12nm) towards the LWS, and to transmit the rest of the visible light to the NGS WFS. In addition, the system will count on an LGS calibration source. The proceeding describes the opto-mechanical design of the LWS System, covering its different subsystems: LWS Dichroic, LWS Sensor and LWS Calibration Unit.